Many electronic devices have characteristics that change with age. For example, the relationship between driving current and light output of light sources such as light-emitting diodes (LEDs); cold cathode fluorescent lamps (CCFLs) and others can change as the light source ages. There is a need for practical methods and apparatus for compensating for such changes to reduce the variation in device performance with time.
In the general case, devices such as LEDs do not degrade linearly with time. This complicates the task of compensating for device aging.
Some patents and patent applications that relate to the aging of devices include:    US patent application publication Nos.: 2008/0258637; 2008/0224966; 2005/110728; 2002/0167474.    PCT patent application publication No. WO 2002/015288;    U.S. Pat. Nos. 7,161,566; 6,995,519; 6,504,565; 6,456,016; 6,414,661; 4,791,632; and    Japanese patent application publication No. 2002/278514A.